Ask HN: How to sell ads to companies?

I have a site with a good amount of visits (but nothing out of this world: 60k visits/month, 150k pageviews/month) but it's part of a niche which I believe is one hell of a market for those companies trying to grab the attention of young people (15 to 30 years old).

My first attempt was to directly reach those big companies and trying to get a sponsorship from them but all I got was a no which was ok.

One of the biggest companies said they weren't interested in being a sponsor but the site was interesting for them so they could buy some ad space there. They told me to contact an agency, I believe they outsource campaigns management to those kind of agencies.

I tried to contact a bunch of them but there was a problem here: they wanted me to sell standard banner sizes and a lower CPM while I was trying to offer them one giant ad (900x400) and bring the whole CPI (cost per influence) to the table. I also said there would only be one ad per page instead of a bunch of them which explains why the CPM was higher than the normal.

I believe this is a far better advertising method for both parties (the companies get more attention to their products and I get a cleaner site, something my users have been appreciating since I started it) but it isn't working.

My question: should I insist on my vision (does it work?) or should I just adapt myself to what everyone does?

I need to learn about other people's experiences on this field.